Such a support assembly is intended in particular to support pipes transporting fluids between a production assembly, situated on the bed of an expanse of water, and a surface assembly.
The fluid transported by the transport pipe is in particular a mixture of liquid or gaseous hydrocarbons, which are collected from wells formed in the bed of an expanse of water.
Known for example from GB 2 295 408 is a facility comprising a support assembly of the aforementioned type.
This facility includes a plurality of parallel transport pipes supported by the support assembly. Each pipe has a lower section formed by a semi-rigid riser suspended by a catenary between the bed assembly and the support assembly.
Each pipe also includes a flexible upper section, designated by the term “jumper,” which connects the support assembly to the surface assembly.
The upper flexible section is in the shape of a J. It is thus capable of damping the relative movements of the surface assembly due in particular to waves, wind, the swell and/or sea currents.
To ensure proper strength of the lower sections, the support assembly includes a buoy completely submerged under the surface of the expanse of water at a sufficient depth for the horizontal movements of the buoy related to the currents and the surface agitation of the expanse of water to be minimal.
To ensure that the supporting buoy is kept in position, the latter part has sufficient buoyancy to create a force moving the buoy toward the surface.
The buoy is also kept in position using anchoring lines that are kept stressed. The lower end of each anchoring line is fastened in the bed of the expanse of water by means of an anchoring assembly.
Such a submerged support assembly is robustly attached and makes it possible to keep the supporting buoy and the pipes in position in a satisfactory manner relative to the bed of the expanse of water.
It is not, however, fully satisfactory. In fact, to ensure an appropriate configuration of the transport pipes, the support must be kept substantially horizontal in the expanse of water. Furthermore, the tension applied on each anchoring line must be adjusted to balance the position of the supporting buoy and prevent certain anchoring lines from undergoing excessive traction forces.
This is made all the more complex by the fact that the anchoring lines are generally provided in pairs, so as to ensure redundancy in terms of security.
It is therefore extremely difficult to precisely predict the length of each anchoring line and the tension that will be applied on each anchoring line once the buoy is submerged in position and all of the anchoring lines are installed.